The local segmental dynamics of anthracene-labeled polystyrene in dilute solution have been studied by using time-correlated single-photon counting. Six solvents covering 2 decades in viscosity were utilized. Correlation times were extracted from the orientation autocorrelation functions and determined as a function of temperature in all solvents. Under good solvent conditions, the correlation time is proportional to at constant temperature, in reasonable agreement with the 1•0 prediction to the Kramers' equation in the high-friction limit. Other aspects of the results are also reasonably consistent with the assumption that the solvent acts as a viscous continuum. As noted in previous investigations, somewhat slower dynamics are observed in -solvents than in good solvents. The potential barrier height for local dynamics extracted from these measurements is 11 ± 3 kJ/mol.

We use frequency-modulated electrostatic force microscopy to track changes in cantilever quality factor (Q) as a function of photochemical damage in a model organic photovoltaic system poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) and 3'H-cyclopropa[8,25][5,6]fullerene-C71-D5h(6)-3'-butanoic acid, 3'-phenyl-, methyl ester (PC71BM). We correlate local Q factor imaging with macroscopic device performance and show that, for this system, changes in cantilever Q correlate well with changes in external quantum efficiency and can thus be used to monitor local photochemical damage over the entire functional lifetime of a PTB7:PC71BM solar cell. We explore how Q imaging is affected by the choice of cantilever resonance frequency. Finally, we use Q imaging to elucidate the differences in the evolution of nanoscale structure in the photochemical damage occurring in PTB7:PC71BM solar cells processed with and without the solvent additive 1,8-diiodooctane (DIO). We show that processing with DIO not only yields a preferable morphology for uniform performance across the surface of the device but also enhances the stability of PTB7:PC71BM solar cells-an effect that can be predicted based on the local Q images.

The phase separation behavior of polymer blends modified by copolymer additives has been studied using light scattering techniques. Block and random copolymers with equal styrene and butadiene content as well as a random copolymer with unequal monomer composition were used as additives at a concentration of 2.5% (w/w). The symmetric additives lowered the phase boundary with increasing concentration while the asymmetric additive destabilized the phase boundary. The data demonstrate a slowing of the kinetics with the addition of any of the copolymers. In comparison to the binary blend, droplet sizes in the early stage were smaller with added symmetric block copolymer and larger with added asymmetric random copolymer. Scaling analysis of the intermediate stage kinetics showed some deviations relative to binary scaling results. Deviations from Porod's law indicate that modifications to the interfacial boundary are most notable for the asymmetric random copolymer. Self-similarity was seen to hold for all of the systems.

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Small-angle neutron scattering measurements were taken from high molecular weight (1.95 X 106) deuterated polystyrene in dioctyl phthalate solution at low concentration (3% weight fraction) under steady shear with rates ranging from the quiescent condition (0 s"1) to 1100 s'1 at room temperature (22 °C).The scattered intensity increased drastically beyond a characteristic shear rate ( = 57 s'1) similar to the increase following a temperature drop from the one-phase region (ambient temperature) to the two-phase region in this upper critical solution temperature system. The cloud point is estimated to be a few degrees lower than 14 °C which is the cloud point for protonated polystyrene in dioctyl phthalate at this molecular weight and concentration. On the basis of this analogy, the random-phase approximation (RPA) approach (the Zimm inverse scattering formula) was used along with a swollen radius of gyration in the Debye function to analyze the data and extract a statistical segment length b and a polymer-solvent interaction parameter Xpe. The segment length was seen to increase slightly, indicating a slight increase in chain volume beyond 7c, while the interaction parameter showed a dramatic increase up to the "spinodal" value -ys = 280 s'1 where the RPA breaks down, therefore giving nonreliable values. This data treatment method has no justification on physical grounds: it is merely a way to quantify our observations since specific models that could explain our data are not available at this time.